This invention relates to a hydraulic control apparatus.
In such a control apparatus known from U.S. Pat. No. 39 71 216 the flow resistance of the nonreturn valve effects an increase in pressure by means of which the pressure compensation valve continuously keeps the pressure in the pump line above the consumer pressure. Since a spring actuation of the closing member of the nonreturn valve remains constant over the whole operational range, the pressure difference between the pressure in the pump line and the pressure in the consumer line remains also constant over the whole operational range. The pressure difference must be designed for the maximum capacity of the consumer so that the maximum power is achieved in the control-position end position of the directional control valve. In intermediate positions of the directional control valve this pressure difference is therefore greater than necessary, resulting in a waste of power which, for instance, causes an increased mechanical load on the pressure medium and the heating thereof.
In German Offenlegungsschrift 37 22 083 which is of a prior date a hydraulic control apparatus is suggested wherein the pressure for the spring side of the pressure compensation valve is increased step by step so as to be able to make use of the maximum power when or shortly before the control-position end position of the directional control valve is reached, and, prior thereto, of only a portion thereof. An infinitely variable increase in the pressure difference for adaptation to the demand of the consumer is not possible.